Packed beds of rock for thermal storage have been used for air-conditioning applications for decades.
Solar thermal energy storage in rock beds is widely used for different applications such as thermal power plants, space heating and cooling and some agricultural purposes for the drying of foods.
Space heating and cooling has been achieved by making use of solar air heaters consisting mostly of an absorber plate, transparent cover and a heat transfer fluid. Air is heated up in the solar heater and the heat may be stored in any thermal storage facility such as a rock bed. As the need arises to use this stored thermal energy, the airstream may be reversed through the rock bed and heat extracted from it.
Evaporative cooling in air spaces has also been used for a long time and has been achieved by forcing air through wetted pads or porous media or by directly spraying water into airstreams.
The problem with existing space-heaters and coolers combined with rock bed storage is that it makes use of an absorber plate heater to heat up the heat transfer fluid (air) to store the energy. Separate evaporative cooling is needed to achieve heating and cooling.